Implementing rotate for save_png

lib/squib/graphics/save_images.rb

@@ -3,8 +3,30 @@ module Squib
 
     # :nodoc:
     # @api private 
-    def save_png(i, dir, prefix)
-      cairo_context.target.write_to_png("#{dir}/#{prefix}#{i}.png")
+    def save_png(i, dir, prefix, rotate)
+      if rotate
+        surface = rotated_image
+      else
+        surface = @cairo_surface
+      end
+      write_png(surface, i, dir, prefix)
+    end
+
+    # :nodoc:
+    # @api private
+    def rotated_image
+      rotated_cc = Cairo::Context.new(Cairo::ImageSurface.new(@height, @width) )
+      rotated_cc.translate(@height * 0.5, @width * 0.5)
+      rotated_cc.rotate(0.5 * Math::PI)
+      rotated_cc.translate(@width * -0.5, @height * -0.5)
+      rotated_cc.set_source(@cairo_surface)
+      rotated_cc.paint
+      rotated_cc.target
+    end
+    # :nodoc:
+    # @api private 
+    def write_png(surface, i, dir, prefix)
+      surface.write_to_png("#{dir}/#{prefix}#{i}.png")
     end
 
   end